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Old 11-25-2016, 04:02 PM   #1
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dual rear axle bus

I saw this this weekend in a field. Up in Everett Washington. Looks like is was getting brakes? Is this person on here. Very cool. I don't remember the details on this design but I had read about them being built for the west coast.

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Old 11-25-2016, 06:12 PM   #2
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Yes, that's a Crown, built in California. If I understand it right, the two rear axles are both driving axles. The engine is in the middle of the bus, under the floor, maximizing interior space. And the engines are big.
Famously durable buses.
It has been said, only part in jest, that Crown went out of business because their buses never wore out.
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Old 11-25-2016, 09:16 PM   #3
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Minor point on terminology that might help if you're looking for more information... "Dual" refers to wheels (two on each side of the axle). If a vehicle has two drive axles, those are "tandems".

And that Crown is a 1977 or newer. You can tell by the thicker post behind the driver's window.
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Old 11-25-2016, 10:15 PM   #4
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Excellent points, Rameses!
And if I may contribute to this little dictionary:

The ring and pinion assembly in a drive axle is sometimes called a screw -- like a propeller on a boat. So, a bus with tandem drive axles can be called a twin screw bus.

If only one of two rear axles is a drive axle, then the other is often called a tag axle. You see tag axles on many modern highway buses, with only one tire on each end of that axle, and the rim turned inward.
A tag axle can be either behind or in front of the drive axle.

And if a tag axle can be lifted off the surface when it is not needed, it is a lift axle -- regardless of number of tires.

Some tag axles can steer. That is, the wheels can turn (as opposed to rotate -- though, of course, they do that also). But they are not controlled by the operator. They simply follow along on the caster principle. This reduces tire wear.

In trucking, when we talk about a truck with one drive axle, we tend to call it a single axle truck.
And a three axle truck we call a three axle.
No such thing as a two axle truck, because that could be misunderstood.
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Old 11-26-2016, 12:57 AM   #5
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That bus is a WA spe'c bus.

If that bus is the bus I think it is it is a Crown Supercoach 2A-426TAC-11--A Supercoach with tandem rear axles, Detroit Diesel 6-71 with a Turbo After Cooler with 11" wide tires (11x20 tires). HP rating was somewhere in the 250-285 HP neighborhood.

If it is the bus I think it is that bus was one of four owned by Edmonds School District that were purchased around 1986.
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Old 11-26-2016, 08:52 AM   #6
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so the second axle on those busses actually drives? its not a tag axle like on most coaches?
-Christopher
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Old 11-26-2016, 09:37 AM   #7
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Originally Posted by cadillackid View Post
so the second axle on those busses actually drives? its not a tag axle like on most coaches?
-Christopher
Yep, tandem drives. Really nice to have in places where it snows!
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Old 11-26-2016, 12:56 PM   #8
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Quote:
Originally Posted by Elliot Naess View Post
. . . . . .
.
.
In trucking, when we talk about a truck with one drive axle, we tend to call it a single axle truck.
And a three axle truck we call a three axle.
No such thing as a two axle truck, because that could be misunderstood.
Elliot has it pretty close. A truck with one drive axle is referred to as a single (drive) axle. A two (drive) axle truck is often referred to as a "tandem" (even if one axle is a tag instead of a drive), to avoid confusion with a truck with one steering, and one drive axle (for a total of 2). The same holds true for trailers. A three axle setup can be called a tri-axle, triple-axle, or "Tri-dem" (many of these setups have at least one lift axle).
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Old 11-26-2016, 06:15 PM   #9
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Quote:
Originally Posted by cowlitzcoach View Post
That bus is a WA spe'c bus.

If that bus is the bus I think it is it is a Crown Supercoach 2A-426TAC-11--A Supercoach with tandem rear axles, Detroit Diesel 6-71 with a Turbo After Cooler with 11" wide tires (11x20 tires). HP rating was somewhere in the 250-285 HP neighborhood.

If it is the bus I think it is that bus was one of four owned by Edmonds School District that were purchased around 1986.
Did WA Crowns also have the Californicated versions of Detroits? Interesting - I thought only CA had them, or was that a CA/OR/WA/West Coast thing? I have a TAC in my bus, but it still develops the same 277HP as the Fed versions - I wonder what the difference is? Injector spray pattern? Turbo A/R?

A friend of mine has a tandem Crown with the 270HP 6-71, I guess also a TAC because it was always a CA bus. With a non-overdrive Road Ranger 10-speed its a surprisingly quick bus - when we brought it back from NorCal it was climbing Tehachapi in 9th gear and passing most trucks.

John
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Old 11-26-2016, 06:31 PM   #10
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Quote:
Originally Posted by Rameses View Post
Yep, tandem drives. Really nice to have in places where it snows!
Tandem Crowns and Gilligs have an inter-axle differential lock that can be used in slippery conditions, but it must be turned off when driving on good road surfaces. Another friend of mine who likes old Crowns bought the first ever Crown tandem school bus, a 1955. Its rear axle arrangement is completely different however - it has a single massive drive axle with a top-loader differential, very military looking, and this is the rear of the two axles. Drive is taken forward to the other drive axle that looks like a dropped-center front axle by means of big drive belts around the hubs. Quite some setup!

John
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Old 11-26-2016, 06:35 PM   #11
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There was nothing stock about any Crown. Every bus was a special order built to a certain spe'c with specific options. Some had black floors, some had the green floors. Some ordered the 6-71TAC at 250 HP and some as high as 285.

I think the different HP ratings were a result of different injectors, timing, and turbo size. I know some had relatively small turbos that spooled up really quickly but didn't have a lot on top. I know others had some pretty large turbos that took a long time to spool up but could really shove some air at high engine speeds.

It all was determined by how much the original owner was willing to spend. If price was not a big factor and you really wanted the big HP you could spe'c the 855 Big Cam Cummins with HP ratings as high as 450 HP. In a school bus! But that option was about $9,000.00 more than the DD 6-71 so it rarely ever was spe'c'ed.

Since a low spe'c Crown was easily $10K more than a rear engine Gillig and about twice the price of an eastern built Type 'D' RE bus a school really had to work hard at justifying the cost of a Crown. To justify an additionaly $9-$15K of additional options was really hard to justify. Particularly on a school bus.

When Edmonds purchased their four Crowns they were able to justify the purchase by putting them onto high density runs that were relatively short which allowed the 15-row buses to be used in a lot of after school activity trips. Those four buses really racked up the miles because they were rarely ever parked.
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